The applicant raises the possibility that NO released from myocytes may be involved in the coronary vasodilation and enhanced myocardial diastolic relaxation observed with adrenergic induced increases in contractility. Accordingly, the applicant plans to test the hypothesis that cardiac myocytes contain a constitutive nitric oxide synthase (cNOS) under the regulation of norepinephrine and other possible endogenous mediators. The applicant will use a NO electrode to functionally characterize cardiac cNOS and pharmacologically dissect this pathway(s) involved in NO release. The specific aims for the project are to definitively demonstrate and functionally characterize cardiac cNOS and to determine the mechanism(s) by which endogenous agonist evoke NO production by cardiac cNOS.